Railroad grade crossing protection system

ABSTRACT

A railroad crossing warning indicator which predicts the time of arrival of trains to a grade crossing is described. Two voltages are derived from the track reactance magnitude and the impedance magnitude and are both indicative of the distance of the train. By summing the difference between the impedance voltage and the reactance voltage with the impedance voltage, a new distance voltage is obtained whereby errors are reduced due to the nonlinearity of the signals due to ballast resistances in the tracks.

United States Patent lnventor Richard V. Pell [56] A l N 3 5 1 UNITEDSTATES PATENTS I pp o.

Filed Feb 26 970 3,246,143 4/1966 Steele et al. 6. 246/128 Patented Oct.19, 1971 Primary Examiner--Arthur L. La Point Assignee MarquardtIndustrial Products Co. Assistant Examiner-George H. Libman Cucarnoug a,Calif.

RAILROAD GRADE CROSSING PROTECTION References Cited Attorney-Robert E.Geauque ABSTRACT: A railroad crossing warning indicator which predictsthe time of arrival of trains to a grade crossing is described. Twovoltages are derived from the track reactance 2 D magnitude and theimpedance magnitude and are both indicaauns rawmg tive of the distanceof the train. By summing the difference U.S.Cl 246/128 between theimpedance voltage and the reactance voltage Int.Cl B61l29/32 with theimpedance voltage, a new distance voltage is ob- Field of Search.246/126, tained whereby errors are reduced due to the nonlinearity of128, 130 the signals due to ballast resistances in the tracks.

-V L OR/sA/ P i l2 TE L i rm ur l Owll i 1 21 :"iJH/E/i fiqA/ofiwss 2652' r-MlLQfi/[A' war/m 3o AMA/r005 8 P/MSC 0zoscwmw \WPCT JuMM/A/G 56A/EW/i 4 H/F/EA I 29m,

CNVIIPWM?) AIM/ 4 75/? ZLDZ'E/Jx) QUAD/P412485 A/VEAT/A/G 1 28- 0555670?ZJF/C'WEA/f/KITO/P cu M l/m6 :g 5g

54 a/sowM/A/qm so [JAKE 56 1 Q Q JUMMWG AMEN/75K 4MP1. //7[/? 44 46 iPfizer/W5 KIM/ 2mm: AELAY VOLTAGL (OM/$424M? filMpL/F/ffi RAILROAD GRADECROSSING PROTECTION SYSTEM BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to warning systems for railroad gradecrossings and more particularly to an improvement in warning predictorsystems used to predict the time of arrival of an approaching train.

2. Discussion of the Prior Art A typical grade crossing predictor is setforth in U. S. Pat. No. 3,246,143 and U.S. Pat. application Ser. No.807,626, filed Mar. 17, 1969, by the same inventor and assigned to thesame assignee as this invention. Much of the same systems electronics ofthat patent are used in the invention discussed herein.

The system of the above patent provides a railroad crossing warningsystem whereby delay to cross traffic is minimized. This is achieved inan arrangement wherein the railroad track is considered as a shortedtransmission line in which the short is provided by the train. Analternating current signal which is a substantially constant currentlevel is applied to the tracks at the location of the grade crossing.The voltage existing across the tracks as the train, and therefore theshort, approaches the grade crossing, will diminish. Thus, the amplitudeof this voltage provides a measure of the distance of the train from thecrossing while the rate at which this voltage diminishes provides ameasure of the velocity of the train. With these parameters it becomespossible to estimate the time of the trains arrival at the crossing.Knowing the time of arrival, the system can start warning signals atsuch a time as will provide the least possible delay to cross traffic.The signal representative of distance and the signals derived therefromrepresentative of velocity are combined to provide a third voltagerepresentative of the time required for the train to arrive at therailroad grade crossing.

It has been found that the input impedance of the shorted railroad tracksection, having infinitely high ballast resistance, varies linearly withtrack length. The Grade Crossing Predictor, as set forth in the abovepatent, for example, uses this principle to develop a voltage which isthe measure of the distance of the train to the predictor probelocation. The voltage is derived from the reactance component of theinput impedance. The rate at which this voltage diminishes as a trainapproaches, provides a measure of the speed of the train. These twovoltages are then combined to estimate the time of the trains arrival atthe crossing. Knowing the time of arrival of the train, the aforesaidsystem can initiate warning signals before the arrival thereof.

Since, in actual practice, ballast resistance is low enough to cause theinput impedance, and in particular the reactance component, to varynonlinearly with track length, an error is introduced into the distancevoltage and thus the speed voltage. These two errors cause the predictorto err in the estimate of the arrival time of the train, thus as theballast decreases, the error increases. Thus, a need has arisen toreduce the error in the estimate of arrival time of a train when ballastresistance is low.

The system as described in the copending application makes use of asecond distance voltage which differs from the first in that it isdeveloped from the impedance magnitude of the input impedance. It isthis second voltage which is used to measure the speed of the train. Thefirst distance voltage is used to measure the distance to a train.

SUMMARY OF THE INVENTION Briefly described, the distance-to-trainvoltage (E is developed in the computing circuit by two other distancevoltages. One of the two voltages which is the reactance voltage (B isdeveloped from the reactive component of the track input impedance. Theother voltage is derived from the impedance component track inputimpedance magnitude. Because of the low ballast resistance, neither ofthese voltages provide an acceptable voltage due to the nonlinearitythereof.

DESCRIPTION OF THE DRAWINGS These and other objects, features andadvantages will become more apparent to those skilled in the art whentaken into consideration with the following detailed description,wherein like reference numerals indicate like and corresponding partsthroughout the several views, and wherein:

FIG. I is a block diagram of the preferred embodiment of the invention;and

FIG. 2 is a graph of the voltage versus distance and the error reductionlinearity realized by this invention.

DESCRIPTION OF ONE PREFERRED EMBODIMENT Turning now to FIG. 1, there isshown a block diagram of the preferred embodiment of this invention. Thetrain I0 has a motion in a direction represented on a pair of trackrails 12.

The train is at a distance L from the origin point P, P, whichrepresents the location of a grade crossing, for example. The trainmotion occurs from left to right. Thevelocity V and the acceleration Afactors are, therefore, represented as going from left'to right on thedrawing. The method of computing the time of arrival is set forth fullyin the aforesaid U. S. Pat. No. 3 ,246,l43 and in the copendingapplication aforesaid.

A computer, in accordance with the aforesaid, includes an oscillator 16which oscillates at a suitable frequency. The output of the oscillator16 is applied to excite a power amplifier 22. A resistor 18 connects oneside of the power amplifier to one of the rails at a point P. The otherside of the power amplifier 22 connects to the other rail P. The poweramplifier 22, together with the resistor 18, comprises a constantcurrent generator. This delivers an input to the track at substantiallya constant current.

It should be appreciated that as the train 10 approaches the points P, Pon the track to which current from the constant current generator isapplied, the impedance of the tracks looking toward the train from thesepoints is continuously being diminished. Thus, the train comprises ashort across the tracks 12, which is moved toward the points P, P. Withcurrent being maintained constant,.the voltage at the points P, P willcontinuously decrease to a minimum when the train reaches the points P,P. Therefore, by measuring the voltage across the tracks 12, anindication is obtained of the distance of the train I0 from the pointsat which the voltage is impressed. The change, with respect to time ofthis voltage, can provide velocity information and a second derivativeof this voltage information provides information as to the accelerationof the train 10.

Accordingly, a narrow band-pass amplifier 26 centered at the frequencyof the oscillator 16, which is connected to the same points of thetracks 12 as the constant current generator, receives a voltagerepresentative of length of track L or distance between the train 10 andthe points P, P. This voltage is an alternating current which ismodulated by the motion of the train I0 toward the points P, P.

The output of the band-pass amplifier 26 is applied to a quadraturedetector 28 which also has a reference input applied from the oscillator16 through a phase shift network 30. The output of the quadraturedetector 28 is applied to a summing amplifier 38. The output of theband-pass amplifier 26 is also coupled to an amplitude detector 32. Theamplitude detector 32 provides a DC voltage proportional to theimpedance of the track 12. The output of the amplitude detector 32provides a voltage E developed by the track input impedance. The outputof the quadrature detector 28 provides a voltage E which is developedfrom the reactive component of the track .input impedance. The -E,,voltage and the 1E voltage are summed in the summing amplifier 33 toproduce E. #ZE E Circuit 34 provides the rate of change of that voltageto produce E =dE /dt. The output of the circuit 34 is coupled through anamplifier 36 to a summing amplifier 38, where it is summed with E Thesumming amplifier 38 receives the time rate of change E of thelinearized distance voltage E from the output of the differentiatingcircuit 34 which is equal to the speed of the train 10. The output ofthe summing amplifier 38 is connected to a high gain amplifier 40. Theoutput of the high gain amplifier is applied to an amplitude comparator42 wherein it is compared with a signal from the reference voltagesource 44. The output of the amplitude comparator 42 is connected to arelay amplifier 46 which operates the warning relay when the signalapplied into it has a sufficient magnitude.

To complete an operative embodiment of the system, an override circuitis also provided, and this includes an amplitude discriminator 52 whichreceives the output from the quadrature detector 28 and compares it tothe output of a reference voltage source 54. The output of the amplitudediscriminator 52 is connected to a relay amplifier 56 which drives aminimum distance override relay 58. The input to the differentiatorcircuit 34 and summing amplifier 38 are voltages proportional to thedistance L between the train and the excitation points P and P. Whendifferentiated, this voltage gives a voltage proportional to trainspeed. The output of the quadrature detector 28 is a voltageproportional to the reactance component across the track which is ameasure of the distance to a train from points I and P.

FIG. 2 illustrates the difference between the distance voltage derivedfrom the reactance magnitude provided by the quadrature detector 28 andthe distance voltage derived from the impedance magnitude provided byamplitude detector 32. The sum of distance voltage E derived from thereactance magnitude and the time rate of change of the linearizeddistance voltage E derived from the reactance and impedance magnitudesis provided by the summing amplifier 38.

When the ballast resistance is very high (R the two distance voltageshave the same slope. When the ballast resistance is decreased (R -1.5ohms, for example, lumped at the predictor) it can be readily seen thatthe slope of the impedance magnitude is much improved over the slope ofthe reactance magnitude, as shown in the two graphs in FIG. 2. Thus, theerror in estimate of the arrival of a train by the predictor is alsomuch improved. The reason that the impedance magnitude provided byamplitude detector 32 is less affected by low ballast resistance thanthe reactance magnitude is apparent in the following example:

Z =R +J X If we assume that R =0.5X, which provides a high ballastresistance condition, then Z ,,=l.l2 X 63.4 If we assume a low ballastresistance condition (R, 2 X) where the ballast resistance is inparallel with Z then therefore, the impedance magnitude Z ,,=0.83/ l .12or a 26 percent reduction in its magnitude while the reactance magnitude4 .83 sin 41.6 1.12 sin 634 IF DT' DX by subtracting, in effect, the Edistance voltage from the E voltage and adds the difference back to theE a more ideal and linear slope is generated as shown in FIG. 2. Thisslope is v nearly as linear at times as the R, slope. This improvedslope gives a more correct calculation of train speed and thus warningtime at grade crossing is more nearly correct.

Thus, there has been provided by the improvements set forth herein atime of arrival predictor computer which has a lower error as comparedto the prior art systems. The output, as provided by this predictor fromsumming amplifier 38, is sent through a high gain amplifier 40 andcompared in a comparator 42 to a reference voltage provided by 44. Ifthe sum of these voltages is above the reference voltage, then the relayamplifier 46 enables a relay 48, which, in turn, either sounds an alarmor lowers a crossing gate, or the like.

Having thus described but one preferred embodiment of this invention,what is claimed is:

l. in a system for deriving from railroad tracks information forpredicting the time required for arrival at a given location of adistant train which is moving on said track towards said location,comprising:

means for applying an AC signal of a constant current level on saidtrack from said location;

means for deriving a first voltage proportional to the reactancecomponent across said tracks indicative of the distance of said trainfrom said location;

means for providing a second voltage proportional to the impedancecomponent across said tracks;

means for providing a voltage developed by the difference between saidfirst voltage and said second voltage;

means for combining said difierence voltage with said first voltage toprovide a linearized distance voltage;

means for differentiating said linearized distance voltage to obtain avoltage representative of the instantaneous speed of said train; and

means for combining said first voltage and said differentiated voltageto provide a third voltage which is a function of the time required forsaid train to arrive at said given location.

2. The system as defined in claim I and further comprising means forutilizing said third voltage for operating a warning device at saidlocation.

3. The system as defined in claim 1 wherein said means for deriving saidfirst voltage is a quadrature detector.

4. The system as defined in claim 1 wherein said means for deriving saidsecond voltage is an amplitude detector.

5. The system as defined in claim 1 wherein said means fordifferentiating is an operational amplifier differentiator.

6. The system as defined in claim 1 and further comprising:

means for providing a reference voltage; and

comparator means responsive to said reference voltage and said thirdvoltage provided by said combining means, said comparator means beingadapted to provide an output when said third voltage exceeds saidreference voltage.

7. The system as defined in claim 6 and further comprising means forutilizing the output voltage of said comparator means for operating awarning device at said location.

8. In a system for predicting the time of arrival of a train on a trackcomprising:

a source of AC signals at a constant current level, said source beingcoupled across said tracks at a selected location;

a quadrature detector adapted to receive signals from said track at saidselected location, said quadrature detector being adapted to provide anoutput voltage proportional to the reactance component across saidtrack;

an amplitude detector adapted to receive signals from said track at saidselected location, said amplitude detector being adapted to provide anoutput voltage proportional to the impedance component across saidtracks;

a first summing amplifier responsive to said amplitude detector and saidquadrature detector for providing a voltage difference between theimpedance output voltage and the reactance output voltage and addingthis difference to the impedance output voltage;

a differentiator circuit responsive to the output voltage of said firstsumming amplifier adapted to provide an output indicative of theinstantaneous speed of said train; and

a second summing amplifier responsive to the output voltage of saiddifferentiator circuit and the output voltage of said quadraturedetector, said summing amplifier being adapted to provide an outputvoltage which is a function of the time required for said train toarrive at said location.

9. The system as defined in claim 6 and further comprising means forutilizing the output voltage of said summing amplifier for operating awarning device at said location.

10. The system as defined in claim 6 and further comprising:

a reference voltage source adapted to provide an output voltage of apredetermined level; and

an amplitude comparator being responsive to the output voltage of thesaid summing amplifier and to the output voltage of said referencevoltage source and being adapted to provide an output signal when thevoltage provided by said summing amplifier exceeds the voltage providedby said reference voltage source.

11. The system as defined in claim 8 wherein said source of AC signalsincludes:

an oscillator adapted to provide an output signal at a predeterminedfrequency; and

a power amplifier coupled between said oscillator and said tracks.

12. The system as defined in claim 11 and further including a band-passamplifier coupled between said track and said quadrature detector andsaid amplitude detector.

13. The system as defined in claim 12 and further comprising means forutilizing the output voltage of said amplitude comparator for operatinga warning device on said location.

14. A system for determining the distance to a vehicle on a railroadtrack which has an electrical current thereon, including;

means coupled to said track for generating a first voltage indicative ofthe track input impedance;

means coupled to said track for generating a second voltage indicativeof the reactance component of said track input impedance;

means for generating a third voltage proportional to the differencebetween said first voltage and said second voltage; and

means for combining said third voltage with said first voltage toprovide a fourth voltage indicative of said distance.

15. The system as defined in claim 14 wherein said means for generatingsaid first voltage comprises an amplitude detec- 1101'.

16. The system as defined in claim 14 wherein said means for generatingsaid-second voltage comprises a quadrature detector.

17. The system as defined in claim 14 wherein:

said means for generating said first voltage comprises an amplitudedetector; and

said means for generating said second voltage comprises a quadraturedetector.

1. In a system for deriving from railroad tracks information forpredicting the time required for arrival at a given location of adistant train which is moving on said track towards said location,comprising: means for applying an AC signal of a constant current levelon said track from said location; means for deriving a first voltageproportional to the reactance component across said tracks indicative ofthe distance of said train from said location; means for providing asecond voltage proportional to the impedance component across saidtracks; means for providing a voltage developed by the differencebetween said first voltage and said second voltage; means for combiningsaid difference voltage with said first voltage to provide a linearizeddistance voltage; means for differentiating said linearized distancevoltage to obtain a voltage representative of the instantaneous speed ofsaid train; and means for combining said first voltage and saiddifferentiated voltage to provide a third voltage which is a function ofthe time required for said train to arrive at said given location. 2.The system as defined in claim 1 and further comprising means forutilizing said third voltage for operating a warning device at saidlocation.
 3. The system as defined in claim 1 wherein said means forderiving said first voltage is a quadrature detector.
 4. The system asdefined in claim 1 wherein said means for deriving said second voltageis an amplitude detector.
 5. The system as defined in claim 1 whereinsaid means for differentiating is an operational amplifierdifferentiator.
 6. The system as defined in claim 1 and furthercomprising: means for providing a reference voltage; and comparatormeans responsive to said reference voltage and said thiRd voltageprovided by said combining means, said comparator means being adapted toprovide an output when said third voltage exceeds said referencevoltage.
 7. The system as defined in claim 6 and further comprisingmeans for utilizing the output voltage of said comparator means foroperating a warning device at said location.
 8. In a system forpredicting the time of arrival of a train on a track comprising: asource of AC signals at a constant current level, said source beingcoupled across said tracks at a selected location; a quadrature detectoradapted to receive signals from said track at said selected location,said quadrature detector being adapted to provide an output voltageproportional to the reactance component across said track; an amplitudedetector adapted to receive signals from said track at said selectedlocation, said amplitude detector being adapted to provide an outputvoltage proportional to the impedance component across said tracks; afirst summing amplifier responsive to said amplitude detector and saidquadrature detector for providing a voltage difference between theimpedance output voltage and the reactance output voltage and addingthis difference to the impedance output voltage; a differentiatorcircuit responsive to the output voltage of said first summing amplifieradapted to provide an output indicative of the instantaneous speed ofsaid train; and a second summing amplifier responsive to the outputvoltage of said differentiator circuit and the output voltage of saidquadrature detector, said summing amplifier being adapted to provide anoutput voltage which is a function of the time required for said trainto arrive at said location.
 9. The system as defined in claim 6 andfurther comprising means for utilizing the output voltage of saidsumming amplifier for operating a warning device at said location. 10.The system as defined in claim 6 and further comprising: a referencevoltage source adapted to provide an output voltage of a predeterminedlevel; and an amplitude comparator being responsive to the outputvoltage of the said summing amplifier and to the output voltage of saidreference voltage source and being adapted to provide an output signalwhen the voltage provided by said summing amplifier exceeds the voltageprovided by said reference voltage source.
 11. The system as defined inclaim 8 wherein said source of AC signals includes: an oscillatoradapted to provide an output signal at a predetermined frequency; and apower amplifier coupled between said oscillator and said tracks.
 12. Thesystem as defined in claim 11 and further including a band-passamplifier coupled between said track and said quadrature detector andsaid amplitude detector.
 13. The system as defined in claim 12 andfurther comprising means for utilizing the output voltage of saidamplitude comparator for operating a warning device on said location.14. A system for determining the distance to a vehicle on a railroadtrack which has an electrical current thereon, including; means coupledto said track for generating a first voltage indicative of the trackinput impedance; means coupled to said track for generating a secondvoltage indicative of the reactance component of said track inputimpedance; means for generating a third voltage proportional to thedifference between said first voltage and said second voltage; and meansfor combining said third voltage with said first voltage to provide afourth voltage indicative of said distance.
 15. The system as defined inclaim 14 wherein said means for generating said first voltage comprisesan amplitude detector.
 16. The system as defined in claim 14 whereinsaid means for generating said second voltage comprises a quadraturedetector.
 17. The system as defined in claim 14 wherein: said means forgenerating said first voltage comprises an amplitude detector; and saidmeans for generatIng said second voltage comprises a quadraturedetector.